The present invention is generally directed to processes for encapsulated toner compositions, and more specifically the present invention is directed to process for the formulation of encapsulated toner compositions by interfacial polymerization of shell-forming monomers in the presence of a free-radical initiator and monomer(s) contained in the core, and the subsequent free-radical polymerization of the core monomers in the absence of a solvent. Thus, in one embodiment the present invention is directed to a process for the simple, and economical preparation of cold pressure fixable toner compositions by interfacial/free-radical polymerization methods wherein there is selected a polymerizable monomer comprising part or all of the core material in place of an undesirable solvent normally used for such processes. Other embodiments of the present invention relate to interfacial/free-radical polymerization processes for obtaining colored toner compositions in the absence of solvents thus eliminating explosion hazards associated therewith; and furthermore, these processes do not require expensive and hazardous separation and recovery steps. Moreover, with the process of the present invention there is obtained improved yields of toner products since, for example, the extraneous solvent component can be replaced by usuable pigment particles, core monomer(s) or core polymer(s). Additionally, the selection of monomer component for the process of the present invention enables a lower cost of production for the desired toner compositions, greater flexibility in the selection of core material properties, and a higher degree of core and toner physical property control than can be achieved with the polymers and solvents of the prior art. The aforementioned toners prepared in accordance with the process of the present invention are useful for permitting the development of images in electrostatographic imaging systems, inclusive of electrostatic imaging processes wherein pressure fixing, especially pressure fixing in the absence of heat is selected.
Encapsulated and cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that fused by heat, primarily relating to the requirements for less energy since the toner compositions used can be fused at room temperature. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fused under high pressure, which has a tendency to severely disrupt the toner fusing characteristics of the toner selected. This can result in images of low resolution, or no images whatsoever. Also, with some of the prior art cold pressure toner compositions substantial image smearing can result from the high pressures used. Additionally, the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions are prepared with solvents that may create explosion hazards; and further these solvents are costly in that separation and recovery equipment is required. Moreover, the selection of the aforementioned solvents may decrease the percentage yield of toner product obtained; and also these solvents limit flexibility requirements in the selection of the core polymer. Additionally, the use of solvents in the prior art processes prevents, in some instances, obtaining toner particles with particular properties. Furthermore, with many of the prior art processes narrow size dispersity particles cannot easily be achieved by conventional bulk homogenization techniques as contrasted with the process of the present invention wherein interparticle free-radical polymerization of partially shell-polymerized toners can be exploited to narrow the size dispersity of the particles thus formed. In addition, many prior art processes provide delecterious effects on toner particle morphology and bulk density as a result of the removal of solvent and the subsequent collapse of the toner particles during particle isolation, resulting in a toner of very low bulk density, which disadvantages are substantially eliminated with the process of the present invention. More specifically, thus with the process of the present invention control of the toner physical properties of both the core and shell materials is afforded by selecting the conditions of the separate polymerization processes and by providing certain polymerization monomers. In this manner, virtually any molecular weight or viscosity property of core materials can be achieved by the proper selection of core monomer(s) and free-radical polymerization conditions. Additionally, the toner compositions prepared in accordance with the process of the present invention have hard shells thus enabling images of excellent resolution with substantially no background deposits for a number of imaging cycles. Also, the toner compositions prepared in accordance with the process of the present invention have apparent bulk densities as high as 1.2 grams/cc.
With further specific reference to the prior art, there is disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there is disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization process are also selected for the preparation of the toners of this patent. Also, there is disclosed in the prior art encapsulated toner compositions containing costly pigments and dyes reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Moreover, illustrated in a copending application U.S. Ser. No. 621,307, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676, the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.
Liquid developer compositions are also known, reference for example U.S. Pat. No. 3,806,354, the disclosure of which is totally incorporated herein by reference. This patent illustrates liquid inks comprised of one or more liquid vehicles, colorants such as pigments, and dyes, dispersants, and viscosity control additives. Examples of vehicles disclosed in the aforementioned patent are mineral oils, mineral spirits, and kerosene; while examples of colorants include carbon black, oil red, and oil blue. Dispersants described in this patent include materials such as polyvinyl pyrrolidone. Additionally, there is described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stablizer irreversibly chemically, or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1, and 2 thereof.
Free-radical polymerization is also well known art, and can be generalized as bulk, solution, or suspension polymerization. These polymerizations are commonly used for the manufacture of commodity polymers. The kinetics and mechanisms for free-radical polymerization of monomer(s) is also well known. In these processes the control of polymer properties such as molecular weight and molecular weight dispersity can be effected by initiator, species concentrations, temperatures, and temperature profiles. Similarly, conversion of monomer is effected by the above variables. None of the aforementioned free-radical polymerization prior art, however, discloses the polymerization kinetics in the core of a microencapsulated toner, especially in the presence of pigments or other additives.
Accordingly, there is a need for the preparation of encapsulated toner compositions. Also, there is a need for interfacial polymerization processes for black and colored encapsulated toner compositions, wherein the core contains a polymerizable monomer and free-radical initiator together with pigments and other materials, and wherein solvents are eliminated. There is also a need for simple, economical processes for the preparation of cold pressure fixable toner compositions in high yields, which processes are effected in the absence of solvents. There is also a need for the formulation of cold pressure fixable toner compositions wherein expensive and hazardous solvent recovery is unnecessary. Additionally, there is a need for simple economical polymerization processes that will permit the generation of encapsulated toner compositions, especially compositions with hard, durable shells, excellent toner flowability and high bulk density. Furthermore, there is a need for improved processes that will enable cold pressure fixable toner compositions with hard shells and soft cores, whose properties such as molecular weight, molecular weight dispersity and degree of crosslinking can be independently controlled. Moreover, there is a need for enhanced flexibility in the design and selection of materials comprising the core and shells of toner particles, and the control of the physical properties, such as bulk density, particle size and size dispersity of the toner, which control is achievable with the process of the present invention. With the free-radical core polymerizations, for example, control of bulk physical properties such as melt viscosity are obtained, for example, by the selection of appropriate monomer(s), and initiator types, and concentrations as well as the use of a certain temperature profile. Thus, the fusing performance of the toner may be altered quite simply by a formulation change, independant of the shell polymerization and material, and without effect on toner durability and flow performance.